Coxsackievirus

A four-year-old girl is brought to the clinic by her mother. A few days ago, the girl began complaining of a sore throat. She was febrile during this time and was not eating very well. Today, she has a rash on her hands. Physical examination shows a restless, well-nourished patients. She seems very uncomfortable, especially upon examination of the oral cavity. There are small grey blisters on the hands and feet, as shown below. Which of the following is the most likely causative agent?